SUMMARY Acute respiratory distress syndrome (ARDS) is characterized by diffuse pulmonary edema that impairs gas exchange and leads to hypoxemia. ARDS can be caused by direct or indirect lung injury from a variety of common conditions including sepsis, pneumonia, trauma, acid aspiration, ischemia-reperfusion, chemical inhalation, and overdistension by mechanical ventilation. Due to its diverse etiology, extremely high hospital case-fatality rates, and poor long-term prognosis, the syndrome has increasingly been recognized by the NIH and biomedical investigators as an important public health concern. Unfortunately, options for treating ARDS remain extremely limited. The only proven methods for enhancing survival are protective, low-tidal-volume mechanical ventilation and prone positioning, both of which are implemented once a patient is in poor enough condition to require intubation. As such, the last decade has witnessed a strong effort among researchers to develop therapies that can prevent lung injury from progressing to ARDS, a trend that has been buttressed by the establishment by the NIH of the Prevention and Early Treatment of Acute Lung Injury (PETAL) multi-site network of clinical trials. A number of promising drugs for ARDS prevention are in the early translational stages of research, including transient receptor potential vanilloid 4 (TRPV4) inhibitors, which block calcium channels whose activation is an important facilitator of pulmonary endothelial hyperpermeability and edema. Administration of these preventive ARDS therapeutics to patients with optimal sensitivity and specificity requires the corollary development of diagnostic tools that can identify individuals who are particularly at risk of progressing to severe lung injury before this progression occurs. In response to this need and in line with the guiding focus of this RFA, the proposed project will develop a molecular probe capable of detecting the early metabolic signs of lung injury before edema develops. Through injecting hyperpolarized (HP) 13C-labeled pyruvate and imaging the subject with magnetic resonance (MR), we are able to track its real-time conversion to lactate and bicarbonate in the lung. Decreased conversion to bicarbonate and increased conversion to lactate indicate mitochondrial dysfunction and upregulated glycolysis, respectively, which have been associated with the endothelial hyperpermeability that allows formation of edema. The first fundamental task of this project will be to demonstrate that HP 13C pyruvate can non-invasively detect lung injury in rodent models before conventional clinical metrics (chest x-ray/computed tomography [CT] to identify edema and alveolar blood gas testing to identify hypoxemia). Second, we will investigate the bioenergetics effects of TRPV4 inhibitors using 13C pyruvate, thereby gaining an idea of how blockage of the TRPV4 channel affects the metabolic characteristics that our probe is measuring. Third, we will assess whether early detection of lung injury pathogenesis using HP 13C MRI and subsequent treatment with a TRPV4 inhibitor generates better outcomes than when the same TRPV4 inhibitor is administered when injury is determined via conventional techniques. Finally, we will evaluate the ability of HP 13C pyruvate to predict endpoints in extracorporeal, perfused human lungs treated with a TRPV4 inhibitor in order to assess the performance of the probe in a human tissue model; the findings of this aim will also have high relevance for the prediction and prevention of lung injury in lung transplant patients.